1. Field of the Invention
The present invention relates to air and other gas decontamination process.
2. Description of Prior Art
Several patents (see for instance U.S. Pat. Nos. 6,245,132 and 6,664,741 and European patent No 1,194,175) have recognized the fact that ionization produced by a set of electrodes can capture contaminant material in a fluid such as air and destroy to some extent certain living biological contaminants. These patents are based on the use of corona electrodes to generate ions and electrically charge the contaminants and then capture the contaminants on an attracting electrode. Other ones are using interaction with a flux of electrons and various absorbing materials to destroy or to sterilize the contaminants. These patents describe different types of electrodes such as wires, needle point, razor blade to form the emitting electrode and flat or cylindrical attracting electrodes.
In particular, European patent No 1,194,175, granted on Sep. 9, 2003 and entitled <<Method for Treating a Gaseous Medium Containing Contaminating Particles>>, is describing a method in which the fluid to be treated is accelerated to form a swirling air vein and made to interact with a first electron flux and then to have the ionized particles interacting with a second electron flux to transform the contaminant into gas. The fluid is then passing through a porous material where chemical reactions occur and where the contaminated gas is transformed into non-toxic gas. The destruction of the contaminant is accomplished through the interaction of the fluid with an accelerated electron flux. The device incorporates some resonant magnetic cavities. No means to achieve such resonance are described. Furthermore no specific means to first extract from the electrodes and secondly to generate an electron flux having specific electrons energy levels are discussed and no means not to generate undesirable by-products such as ozone or NOx are addressed or claimed. The device is using a DC potential. No means to prevent arcing of the device are discussed.
U.S. Pat. No. 6,664,741, granted on Dec. 16, 2003 and entitled <<Method of and Apparatus for Electrostatic Fluid Acceleration Control of a Fluid Flow>>, recognized that in order to increase the ions generation at the electrode it is advantageous to increase significantly the electrode AC current component. To achieve this the patent is using electrodes with a significant capacitance feed by a DC switching power supply having a relatively large ripple voltage component producing the AC voltage excitation to the electrode capacitance. The AC current generated is being defined by the AC voltage of the ripple divided by the impedance of the electrode capacitance at the switching frequency. The AC current is thus proportional to that AC voltage and to the electrode capacitance at a specific switching frequency. One draw-back is that the electrodes require a relatively large capacitance to generate any significant current to improve the efficiency considering also that the power supply switching frequency is limited. Also the large AC voltage component superposed on the DC supply modulates to some extent the electron energies in the discharge.
U.S. Pat. No. 6,245,132, granted on Jun. 12, 2001 and entitled <<Air Filter with Combined Enhanced Collection Efficiency and Surface Sterilization>>, is using a basic filter that is sandwiched between two electrodes fed by a DC or AC or RF electrical source. The DC electrostatic field is used to attract the contaminant biological material, and intermittently a sterilization field using an AC or DC or RF source of enough intensity is applied to generate a surface plasma and thus destroying the contaminant biological material. No specific means for increasing the discharged current without increasing the electrical potential is described.
European patent No 0,600,101, granted on Jun. 8, 1994 and entitled <<Device for Biological Cleaning and Filtration of Air>>, is using corona discharging electrode and a non-discharging electrode to produce ions. The discharging electrode being a needle supplied with a large DC potential. Porous material is used in line of the airflow and an electrostatic precipitator is used to retain the contaminants. However, it does not provide an efficient current of particular electron energy level to destroy the contaminants or to control unwanted by-products.
International patent application WO 02/49767, published on Jun. 27, 2002 and entitled <<Electrostatic Device for Ionic Air Emission>> is suggesting a specific geometry of the receptive electrode, in a corona discharge system, to improve and make the collection of contaminants more homogeneous over the electrode surface thus improving its efficiency. It does not provide specific means to control the ions energy generation or the energy level.
U.S. Pat. No. 5,077,500, granted on Dec. 13, 1991 and entitled <<Air Transporting Arrangement>>, covers a specific geometry of the electrodes and the use of a dual power supply arrangement where one power supply controls the ions generation and the second one their acceleration. The system's description does not propose any resonant mechanism to generate the ions and does not address the control of any specific energy level to avoid generating undesirable by-products.
U.S. Pat. No. 6,504,308, granted on Jan. 7, 2003 and entitled <<Electrostatic Fluid Accelerator>>, covers some specific geometries of corona discharge accelerating and shielding electrodes to improve an electrostatic fluid accelerator. Although is it mentioned that it will not produce substantial undesired ozone and nitrogen oxides when the fluid is air, it is not described how this can be achieved. Reference is strictly made to a voltage setting within two extreme limits: “a voltage between the said corona electrodes and said exciting electrodes is maintained between the corona on set voltage and the breakdown voltage”. With this technology, in order to generate a significant amount of ions, an extremely large electrical field must be generated at the tip of the corona electrodes. This very large electrical field produces high-energy particles that are susceptible to generate undesired by-products. A compromise is thus made between the quantity of ions generated and the production of undesired by-products.